1. Field of the Invention
The present invention relates to a spread illuminating apparatus particularly used as an illuminating means for a liquid crystal display.
2. Description of the Related Art
A demand for a liquid crystal display has been increased mainly for personal computers and mobile phones since the liquid crystal display which operates at low power consumption features low profile and light weight. Since a liquid crystal which is a component member of the liquid crystal display does not emit light by itself unlike a light emitting element such as a cathode ray tube, an illuminating means for illuminating the liquid crystal for use in a dark place is required. In particular, in the recent demand for lower profile and smaller power consumption, there has been a growing tendency to employ a spread illuminating apparatus of side light type (light conductive member type) as an illuminating means for illuminating the liquid crystal display.
FIG. 5 illustrates a spread illuminating apparatus of side light type, particularly intended for increasing brightness. A spread illuminating apparatus 1xe2x80x2 is generally composed of a transparent substrate 4 disposed so as to cover a surface 3 (an observation surface) of a liquid crystal device 2 with a lower surface 14 facing the surface 3, and a light source 6 disposed along an end surface 5 of the transparent substrate 4. The transparent substrate 4 is made of a highly light-transmissible material, shaped like a flat plate and substantially rectangular in section. A light reflection pattern 15 is formed on a surface 13 (an upper surface) of the transparent substrate 4. The light reflection pattern 15 is formed parallel to the end surface 5 and composed of a plurality of grooves 16 substantially triangular in section and a plurality of flat portions 17 adjacent to the grooves 16. In order to uniform light emitted from the light source 6, the ratio of the width of the grooves 16 to the width of the flat portions 17 is set to increase in proportion to the increase in distance from the end surface 5 of the transparent substrate 4.
The light source 6 is generally composed of a bar-like light conductive member 7 made of a transparent material and disposed along and close to the end surface 5 of the transparent substrate 4, and a spot-like light source 8 disposed facing one end of the light conductive member 7. Moreover, an optical path conversion means 11 is provided on the light conductive member 7. The optical path conversion means 11 is formed on a surface 10 opposing a surface 9 facing the end surface 5 of the transparent substrate 4 such that grooves, for example, triangular in section run in the thickness direction of the transparent substrate 4, or that surface roughening is partially provided whereby light emitted from the spot-like light source 8 is made incident on the end surface 5 of the transparent substrate 4 in a substantially uniform manner. Further, in order to achieve a uniform emission of light from the bar-like light conductive member 7, the depth of the grooves triangular in section preferably increases in proportion to the increase in distance from the spot-like light source 8.
Also, in FIG. 5, two light sources 6 are disposed along and parallel to the end surface 5 of the transparent substrate 4 (hereinafter one located far from the transparent substrate 4 is referred to as xe2x80x9couter light sourcexe2x80x9d and the other located close to the transparent substrate 4 as xe2x80x9cinner light sourcexe2x80x9d). Light emitted from the outer light source 6 passes through the light conductive member 7 of the inner light source and enters the end surface 5 of the transparent substrate 4. Thereby, the amount of light incident on the transparent substrate 4 is increased, and the brightness of the screen can be improved compared with a case where only one light source 6 is provided.
Further, as in a spread illuminating apparatus 1xe2x80x3 shown in FIG. 6, two light sources 6 may be disposed along both the end surface 5 of the transparent substrate 4 and an end surface 25 opposite to the end surface 5, respectively. In this case, the ratio of the width of the grooves 16 to the width of the flat portions 17 is set to be maximum at a center portion of the transparent substrate 4. In addition, in order to introduce a still larger amount of light from the light source 6 into the transparent substrate 4, a light reflection member 19 may be provided so as to cover the respective light conductive members 7.
The light conductive member 7 is formed into a wedge-shape in such a manner that the area of an end surface 12xe2x80x2 opposite to an end surface 12 facing the spot-like light source 8 is smaller than that of the end surface 12, whereby light leakage at the end surface 12xe2x80x2 is reduced. Accordingly, light enters efficiently the transparent substrate 4, thereby improving the brightness of the screen. Here, in the wedge-shaped light conductive member, an end including the end surface 12 having a larger area is referred to as a xe2x80x9clarge endxe2x80x9d, and another end including the end surface 12xe2x80x2 having a smaller area is referred to as a xe2x80x9csmall endxe2x80x9d.
The spread illuminating apparatuses 1xe2x80x2 and 1xe2x80x3 shown in FIGS. 5 and 6, respectively, include the following problems. Specifically, the two light sources 6 are disposed at the respective end surfaces 5 and 25 of the transparent substrate 4 for the purpose of improving the brightness of the screen. And, light emitted from the outer light source 6 of the two light sources 6 disposed parallel to each other passes through the light conductive member 7 of the inner light source 6 and enters the end surface 5 of the transparent substrate 4.
However, light which is emitted from the outer light source 6 passes through the light conductive member 7 of the inner light source 6 and enters the end surfaces 5, 25 and light which is emitted from the inner light source 6, travels in the light conductive member 7 of the inner light source 6 and enters the end surface 5, 25 interfere with each other. This generates interference fringes resulting in that intensity of light entering the transparent substrate 4 is made non-uniform in the longitudinal direction of the light source 6. Further, disposition of the two light sources 6 in parallel at the respective end surfaces 5 and 25 of the transparent substrate 4 is unfavorable in view of a demand for downsizing the light source, and effective countermeasures have been desired.
The present invention has been made in view of the above, and an object of the present invention is therefore to realize uniform light emission and high brightness as well in the spread illuminating apparatus while not increasing the size of the light source so as to meet the recent demand for downsizing and power saving.
According to a first aspect of the present invention to solve the above problems, in a spread illuminating apparatus of side light type having two bar-like light sources disposed on an end surface of a transparent substrate made of a light-transmissible material, the two light sources each comprising a bar-like light conductive member made of a transparent material and a spot-like light source disposed at one end of the light conductive member are disposed to overlap with each other in the thickness direction of the transparent substrate with respective spot-like light sources opposing each other.
In accordance with the present invention, light emitted from one spot-like light source into one light conductive member of the two directly therefrom enters the transparent substrate without passing through the other light conductive member and vice versa. Thus, light coming out from the one light conductive member and light coming out from the other light conductive member do not interfere with each other so as to prevent generation of interference fringes. Further, since the two light conductive members are disposed so as to overlap with each other in the thickness direction of the transparent substrate, the installation range of the light source does not expand in the direction orthogonal to the longitudinal direction of the light conductive members.
According to a second aspect of the present invention, in the spread illuminating apparatus of the first aspect of the present invention, the two light conductive members are each formed in a wedge-shape having a large end and a small end and are disposed so as to overlap with each other with the large end of the one conductive member aligned to the small end of the other light conductive member and vice versa. In this configuration, light entering the large end and traveling in the light conductive member is prevented from leaking from the small end and can be effectively introduced into the transparent substrate. In addition, the total dimension occupied by the two light conductive members can be held down from increasing in the thickness direction of the transparent substrate.
According to a third aspect of the present invention, in the spread illuminating apparatus of the second aspect of the present invention, the two light conductive members are each formed in a wedge-shape such that the dimension at least in the overlapping direction is changed. Thus, the dimensional increase in the thickness direction of the transparent substrate due to overlapping the two light conductive members can be held down.
According to a fourth aspect of the present invention, in the spread illuminating apparatus of any one of the first to third aspects of the present invention, the thickness formed by overlapping the two light conductive members is equal to or smaller than the thickness of the transparent substrate, resulting in downsizing. Also in this configuration, light coming from the light conductive member does not leak outside the transparent substrate and can be efficiently introduced into the transparent substrate.
According to a fifth aspect of the present invention, in the spread illuminating apparatus of any one of the first to fourth aspects of the present invention, the two light sources are disposed along an end surface of the transparent substrate and another end surface opposite thereto, respectively. And, the above end surfaces are illuminated by the corresponding light sources, respectively, thereby making light emission more uniform and brightness higher in the spread illuminating apparatus.